Fire retardant acoustical tile



Sept. 10, 1963 R. F. coTTs 3,103,444

FIRE RETARDANT ACQUSTICAL TILE Filed Dec. 30, 1960 (1rd ROXYL Ooxmm o mum/van slucmv PERCENT SIIITINKflGE IN THE/N555 0NLY 1 an: a /0 03 I -Z 3 .4-

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United -States Patent 3,103,444 I FIRE RETARDANT ACOUSTICAL TILE Ronald F. Cotts, Evanston, Ill., a'ssignor to The Celotex Corporation, Chicago, 111., a corporation of Delaware Filed Dec.'30, 1960, Ser. No. 79,772

7 Claims. (Cl. 106-71) This invention concerns an acoustical ceiling-tile and more particularly, a fire retardant acoustical ceiling tile. In contemporary residential, industrial, commercial, and particularly institutional construction, it is necessary to obviate the hazards to life and property caused by the ravages of fire. To this end, in those installations wherein acoustical or, sound absorbing ceiling tile is installed, it is necessary to insure that the ceiling tile be fire resistant so as to reduce the risk of firedamage. In the course of installing acoustical tile, a suspension system of some type must be employed; In many installations, the usual type of suspension system involves the use of a number of individual ceiling tiles kerfed on four sides and the insertion of conventional T-splines in the kerf-s. The T-splines are supported from a surface above the ceiling. It is apparent that-if the individual tiles shrink excessively because of the heat generated in a fire, they may fall out oflthe suspension system and permit flame or hot gases. to penetrate to the area-above the ceiling. In addition, the internal bonds which hold the individual ascoustical tiles together are weakened by'fire and the tiles become crumbly and fall out of the suspension system. u I

-A particular type of ascoustical tile, and the type to. which this invention pertains, is made of granular mineral fibers with a binder. Granular mineral fibers may be defined as mineral wool or glass wool the form of granules or separate tufts which are incontradistinction to felted or interlaced mineral wool. The conventional mineral fiber tile made of .granular mineralwoolwith a starch ice,

2 It is yet another object ofthe'presentinvention to set forth a method for making an improved granular mineral fiber acoustical tile. a

Other and fiurther objectsand advantages of the invention will be apparent on reading the following specification in conjunction with the accompanying drawings, in

. which:

binder. shrinks substantially in thickness when subjected to a high temperature condition, such as that occurring during a fire. The 'tile does not'shrink appreciably in length or width. It is thought that the action of. the granular mineral fiber tile in shrinkinggreatly in thickness and not appreciably in length or Widthis dueto the minimum level of interconnectingyfibers between granules and the lwge ratio of granule diameter to the thickness. When heated sufiiciently, the fiberssoften and tend .to shrink and coalesce, and the fiber granules are readily distorted from spheres to oblate spheroidsby the gravitational forces in the vertical direction. In becoming oblate spheroids, the granules tend "to bulge outwardly in the horizontal plane and thus the shrinkage in'length and width is negligible. However, in the vertical plane the shrinkage of the tile is appreciable.

In order to strengthen the acoustical tile against such shrinkage, the addition of certain types of clay or clay-like material to the binder formulation in the manner of the present invention has been found to be efiective. The clay particles have a minimal effect in strengthening the granules and binder until the tileis heated or fired by the rise in temperature due to a fire. Under these latter conditions, the clay particles inhibit shrinkage by raising the fusing point of the mineral fibers. The clay bonds the glass mineral filber pellets together and also prevents shrinkage of the individual granules;

It is, therefore, an object of the present invention to provide a granular mineral fiber acoustical tile which has greater bonded strength'when subjected to fire than conventional acoustical tile. 7

It is another object of the present invention to provide a granular mineral fiber tile which remains in place in a' suspension system under conditions of extreme heat.

FIGURE 1 is a cross-section of a tile made in accordance with the invention;

FIGURE 2 is a' molecular diagram of an ingredient suitablefor the invention, and 1 FIGURES 3 and 4 are graphical representations useful in explaining the invention. i v Referring now to FIGURE 1, there is shown an acoustical tile 10 suspended by means of T-splines 11. Granules 12 of mineral wool are shown interspersed within tile 10. The granules 12 are held in place by a binder, such as starch, inwhich particles of clay are suspended. Additionally, the clay particles adhere to the individual fibers of the mineral wool.

In considering the types of clay which may be used in the binder, non-swelling clays of the kaolin or non-swelling type are especially preferred. These clays are widely available, relatively low in cost, and'easily procured in commercial quantities. Their non-swelling characteristics prevent problems of undue thickening of the binder which occurs witlithe swelling type of clay. I

.Montmorillonites, including bentonite and particularly sodium bentonite, are of the swelling type of clay and they hold large quantities of bound water. Thus, the drying problems in the manufacture of the fire resistant acoustical tile of the invention are increased. a In addition, the addition of the swelling type of clay does not produce the high temperature bonding characteristics of 'In the caseof Kaolex D-6, the thickness of each layer is about 7. 15 angstrom units. 7

All kaolin minerals are composed of identical layers of composition Al O .2SiO .2I-I O- and differ only in the way the layers are arranged with respect to each other.

'The chemical representation of a kaolin layer is i2 5) z( H)4 V v V implying sheets of n(Si O linked to sheets of n(Al (OH) units. This'unit is. of indefinite length in two directionswalon-g the a and b crystallographic axes.

Kaolin contains many layers stacked above each other to give extension'along the c-axis. Thus, with reference to FIGURE 2, the single layer along the c-axis may be represented as "therein shown.

In pnacticing the invention, the clay is pulverized so that the plates are several hundred layers in thickness and are preferably about 300 to 800 times the thickness of the single layer. such that its length and width are about 10 times, the thickness or about 21,000 to 57,000 angstrom units, or about 2.14 to 5.72 microns. i

Other minerals which contain magnesium ions in single layer silicate structure are also useful in supplying the fire retardant feature of the present invention. Such a mineral is chrysotile which is a common constituent of asbestos:

However, again it is important to note that.

minerals. the chrysotile plates used in the present invention are not of the long fibrousfilamentary type of asbestos, but must i be pulverized to the fineness of the kaolin. Thus, the

chrysotile layers must be about 21,000 to 60,000 angstrom units in length and width and about 7.33 angstrom units thick.

Talc or similar type of kaolin clay, a major component.

The area of the plate, as pulverized, is

of soapstone, if finely ground, may also be used. Ball clay may also be used. 1 i

The diameter of the mineral fiber filaments is in the order of 2. to 12 microns, so that the length of the clay plate in any' direction is less than the diameter of the tion does not aid or enhance the strengthening of the fiber filament attributable to the clap plate.

- GRANULAR MINERAL WOOL The mineral fiber acoustical ti'le of the present invention is made' by making mineral .fiber granules. These maybe made 'by any conventional process known to those skilled in the art. Forja clear understanding of the general procedure of the formation of mineral or glass wool by blowing with the collection of blown wool as a loose blanket, and for an illustration of a procedure'for tearing tufts or agglomerates therefrom, as has above been referred to, reference is made to the patent toCoss, 2,375,284. This tator is then switched to low speed. The cooking vessel is heated until the temperature of themixtu-re is 185 and until the viscosity of the gel mixture is 1000/2000 centipoises as measuredby'a Brookfield viscosimeter at 170 F. After the cooking step, the gel is stored in the cooker tank wherein the temperature of the 'gel may be allowed to decrease to 170 F. V v

The method of forming the acoustical tile comprises mixing together approximately 200 pounds of mineral wool fiber .in granulated form and-about 116 gallons of the binder as preparedin the previously 'describedman ner. The binder is pumped into a tank until 116 gallons are measured therein and the mineral wool fiber is delivered to the tank'by a conveyor belt. The binder and mineral wool fibers are then thoroughly mixed by an suit-' able mixing device so that a complete inter-mixture of the binder and mi-n'eral wool is achieved.

Following thismixing operatiomthe totally mixed min- 7 eral wool fiber and binder is then fed onto paper-lined patent schematically shows a loupola or melting furnace,

the jet or blast for blowing the moltenmaterial into fiber, and a wool room .in which the fiber settles as a blanket on a conveyor running across the bottom of the wool room. This patent also shows what is termed a stationary rack and a rotatable paddle rack which might be termed complementing combs which serve, as the paddle rack or rotatable comb revolves, to tear small granules or tufts of fibers from the blanket of fibers and deposit them on a conveyor.

. BINDER Atypical binder formulation is:

Pounds Percentage Dry Basis Paraffin wax Calrnn I Kaolex D-fi clay Total -l if desired, the-binder my be formulated with the addition thereto of a filler in an amount of about 8% by weight of dry solids. The cfiller preferably consists of pulverized dust from reject acoustlcal'tile made according to the method set forth herein. The addition of the filler tends to thicken the binder somewhat, and as a consequence the amount of tufted mineral wool fibers may be slightly reduced.

METHOD OF -MAKTNG TILE I The procedure for mixing and cooking the binder per of water, Calgon, boric acid, clay andstanch is added to the cooking vessel and the remainder of the hot water at 210 F. The agitator is continued at high speed through a 10 minute cooking period, whereupon the agiplatens and leveled to thedesired thickness by a reciproeating screed bar. The purpose of the screed bar is to produce fissures in the surfaceof the tile so as to aid in increasing the sound absorptionefliciency thereof.

Following the molding of the tile, the molded slabs are air-dried in the open air before being placed in the drying oven. Approximately one hour air-drying tempera ture has been found to. be desirable. Following the airdrying, the molded slabs are placed in ovens for a drying cycle of from 12 to 13hours for thick slabs. The drying oven'is divided into four zones in which the temperatures of the respective Zones for A" thick tile arev as follows:

Zone 1 Zone 2 Zone 3 Zone 4 Calgon: Sodium hexametaphosphate, a commercial grade.

Boric acid: Granular, technical grade. Paraifin wax: Fully refined parafiin-133'-135 F. :M.P. Starch: Commen'cal grade.

As has been indicated herein of non-swelling clay may be used the acoustical tile. tic-a1 tiles made with erals, reference may be had to the following table:

Table I To illustrate the shrinkage of acous- Percent Percent Shrinkage Shrinkage in Length in Thickness Control Board (no clay) 2. Tile with 0.6 pound of kaolin (Kaolex D6) 2. Tile with 0.5 pound pulverized chrysotile 2 Tile with 0.5 pound magnesium silicate (talc) 1 g as compared to the 50% shrinkage of the control board whichcontained no clay. In Table I the amount of clay is given for an acoustical tile thick and 12 X before, different types in the manufacture of similar amounts of different clay min-' 5 7 12" in area. Here the amount of clay is approximately 25% by weight of the amount of mineral wool, and is consistent with the formulation given thereinbefore.

To illustrate the improvement in the percent shrinkage in thickness in terms of the amount of clay added, reference may be had to the graph of FIGURE 3, wherein the percent shrinkage in thickness is plotted as the ordinate axis of the amount of clay as abscissa.

It may be seen that as the amount of elay is increased from pounds to 0.05 pound, the percent shrinkage ininlcreases. As the amount of clay isincreased from 0.0 5 pound to 0.4 pound, the percent shrinkage in thickness unexpectedly decreases rapidly to about 8%. The curve has not been extended because this amount of clay is the amount prefenred for actual production.

' However, reference to Table I shows that an increase of clay to 0.5 pound again reduces the percent shrinkage to 3.2%. This latter figure is consistent with the graph of FIGURE 3.

Referring now to FIGURE 4, there .is therein shown the relationship between the amount of kaolin clay added and the percentage of shrinkage in length of the acoustical tile. It may be seen that as clay is added up to about 0.1 pound for an acoustical tile /8 thick and 12 x 1 2" in area, the percentage of shrinkage increases. Then, for the addition of kaolin clay from 0.1 pound to 0.2 pound, the percentage of shrinkage remains high. For the addition of clay from about 0.2 pound to 0.4 pound, the shrinkage in length unexpectedly decreases. Consequently, it is seen that in considering the shrinkage in either thickness or length, the amount of clay to be added should be about 25 by weight of the amount of mineral wool and not less than about 12% by weight. In summary, there has been set forth a new and novel acoustical tile made of granulated mineral fiber which, by the addition of non-swelling clay particles to itsbinder, has a remarkable resistance to shrinkage in thickness. Such tile affords added protection from fire damage.

While there has been set forth and described embodiments of the novel fire resistant acoustical tile of the invention, other modifications and changes may occur to those skilled in the art, and it is intended to include such modifications and changes in the scope of the appended claims.

I claim:

'1. An acoustical tile consisting essentially of tufts of mineral fibers, and a binder in which said tufts of mineral fibers are uniformly dispersed, said binder consisting essentially of starch, wax, boric acid and a finely ground non-swelling silicate mineral selected from the group consisting of kaolinite, talc, ball clay and chrysotile plates, said silicate mineral being in an amount not less than 12% by weight of the mineral fibers.

2. An acoustical tile consisting essentially of tufts of mineral fibers, said fibers having a diameter of between 2 and 12 microns and a binder in which said tufts of min- -particles of a non-swelling silicate mineral selected from the group consisting of kaolinite, chrysotile plates, ball clay and talc, wherein said particles of silicate mineral are less in any dimension than said diameter of said mineral fibers and in an amount not less than 12% by weight of the mineral fibers.

4. An acoustical tile consisting essentially of tufts of mineral fibers, said fibers, having a diameter of 2 to 12 microns and a binder in which said tufts of mineral fibers are uniformly dispersed, said binder consisting essentially of starch, wax,'boric acid, and finely ground discrete particles of non-swelling silicate mineral, said particles being in the form of between 300 and 800 layers of sheets of SL 0 linked to (Al (Ol-l) units, said particles having at least one dimension normaal to said layers of a length about 10 times the total thickness of said layers, said particles being in an amount not less than 12% by weight of the mineral fibers.

5. An acoustical tile consisting essentially of tufts of mineral fibers and a binder in which said tufts of mineral fibers are uniformly dispersed, said binderconsisting essentially of starch, wax, boric acid, and finely ground dis crete particles of non-swelling silicate mineral selected fnom the group consisting of kaolinite, chrysotile plates, ball clay and talc, in an amount substantially oneourth by weight of said mineral fiber in said tile.

6. A binder composition for an acoustical tile consisting essentially of 36 percent of starch, 7 percent of boric acid, 5 percent of paralfin wax, a minute amount of sodium hexametaphosphate, and 52 percent of finely gmound particles of non-swelling silicate mineral from the group consisting of kaolinite, talc, ball clay and chrysotile plates, wherein said particles of silicate mineral are less in any dimension than 7 microns.

7. A binder composition for an acoustical ti-le consisting essentially of 36 percent of starch, 7 percent of boric acid, 5 percent of parafiin Wax, and 52 percent of finely ground particles of non-swelling silicate mineral selected from the group consisting of kaolinite, chrysolite piates, ball clay and talc, wherein said panticles of silicate mineral are less in any dimension than 7 microns.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN ACOUSTICAL TILE CONSISTING ESSENTIALLY OF TUFTS OF MINERAL FIBERS, AND A BINDER IN WHICH SAID TUFTS OF MINERAL FIBERS ARE UNIFORMLY DISPERSED, SAID BINDER CONSISTING ESSENTIALLY OF STARCH, WAX BORIC ACID AND A FINELY GROUND NON-SWELLING SILICATE MINERAL SELECTED FROM THE GROUP CONSISTING OF KAOLINITE, TALC, BALL CLAY AND CHRYSOTILE PLATES, SAID SILICA MINERAL BEING IN AN AMOUNT NOT LESS THAN 12% BY WEIGHT OF THE MINERAL FIBERS.
 6. A BINDER COMPOSITION FOR AN ACOUSICAL TILE CONSISTING ESSENTIALLY OF 36 PERCENT OF STARCH, 7 PERCENT OF BORIC ACID, 5 PERCENT OF PARAFFIN WAX, A MINUTE AMOUNT OF SODIUM HEXAMETAPHOSPHATE, AND 52 PERCENT OF FINELY GROUND PARTICLES OF NON-SWELLING SILICATE MINERAL FROM THE GROUP CONSISTING OF KAOLINITE, TALC, BALL CLAY AND CHRYSOTILE PLATES, WHEREIN SAID PARTICLES OF SILICATE MINERAL ARE LESS IN ANY DIMENSION THAN 7 MICRONS. 